The present invention relates to a radiographic phosphor screen to be used as an intensifying screen, a direct viewing fluorescent screen, photofluorographic screen and an input screen of an image intensifier tube for X-ray or radioisotope, or to be used for nondestructive inspection of metal articles or for metal article detectors.
In the medical science, radiology using X-rays or .gamma.-rays has made rapid and drastic progress, and various radiographic apparatuses for the medical diagnostic system have been developed in succession. In these apparatuses, radiophosphor screens are used for converting X-rays and .gamma.-rays to visible rays and/or ultraviolet rays. In the medical diagnosis using radioactive rays, especially when radioactive rays are applied to human bodies, it is necessary to reduce dosages of radioactive rays for safety.
Calcium tungstate (CaWO.sub.4) and terbium-activated lanthanoid oxisulfide phosphors have heretofore been used for conventional radiographic screens. In these phosphors, the overall efficiency depends on a lot of factors, such as the X-ray absorption efficiency, the efficiency of conversion of absorbed X-ray energy to light energy and the matching of the emission spectrum of the phosphor with the spectral sensitivity of the detector. The second efficiency is relatively low in calcium tungstate phosphors and the third efficiency is comparatively low in terbium-activated lanthanoid oxisulfide phosphors in the case of usual blue-sensitive medical X-ray films.